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Unread 12-06-2013, 04:45 PM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default Re: Vorshlag Shop Truck - 5.3L SWB GMT800

continued from above

The original front calipers were already a twin piston sliding caliper but we had to upgrade those as well as the slider assembly, to move them and the pad outboard 1/2" to match the 1" larger diameter of the rotor. We went through several more sets of front brake pads before finding the right one for that (multiple pad shapes and thicknesses). As we also found there was a substantial brake hose change as well, which the forums neglect to mention.

I asked Kyle to mock up the front and rear discs and calipers first before we started chasing after the correct pads. Of course this is our shop truck and I wanted it to be a bit more "showy" so I ordered the red powder coated Powerslot versions of the calipers/sliders as well as the slotted/drilled/zinc plated Powerslot versions of the rotors. It is a little blingy but hey, that's part of the upgrade path on our shop truck.

That's the dimensions on the front and rear rotors we went from and to, above. The front rotors on the typical 4 wheel disc GMT800 were this 12.00" diameter x 1.18" (29mm) thick 6-lug unit. The 13.00" x 29mm front rotor were picked up plus the matching caliper slider brackets and new front calipers as well. Going up a full inch in diameter is huge. Maybe we could have used the old front calipers (although they look fairly different) but with 240K miles I wasn't going to chance it, so instead of rebuilding the old stuff I got the matching '05-06 13" rotor's calipers. On the rear there was a tiny rotor diameter increase but the later GMT800 SUVs had that much thicker rear rotor, going from 20mm to 29mm thick. These SUV rear discs were also equipped with twin piston sliding caliper instead of the normal single piston units, so we got these calipers plus the matching slider brackets.

I suppose we could have gone Centric Premium rotors for a few bucks less per corner, but it wasn't much more cost to bling it up a bit with the "Powerstop" versions. The Powerstop rotors are slotted and drilled (and the holes are heavily chamfered) and included a silver "clear zinc" electroplating over the entire rotor surface. I'm not so keen on the drilled holes part, but a plated rotor is nice, as it doesn't immediately start to rust on the hub face and other areas where an unplated cast iron rotor would (just look at the old rotors at the top of my post). These are all fully rebuilt calipers so they have new dust boots and caliper seals, and came with the pad retention clips. And they look purdy...

The mock-up of one front and rear corner (see above) with the rotors, slider brackets and calipers went well so I had the guys move ahead and order brake pads. Lots of deliveries later... three sets of rear pads and two sets of front pads is what it took to get the right shape and thickness, and we noted the part numbers to use. We ended up with Brembo ceramic pads which stop quietly and work dead cold.

Left: The rear dust shields need to be trimmed or removed to clear the larger calipers. Right: Front brake flex hose was totally different

A few other things needed to be changed for a 100% perfect brake install. First thing I noticed when I looked at the rear calipers and rotors was a pinched dust shield. Since the twin piston caliper is longer the normal "cut out" section for the old caliper was too small. I had the guys just trim the old dust shield to fit the longer rear calipers, but if we were to do this again we would order new OEM rear dust shields from the later SUV we robbed the rotor and calipers from. Next, I had a feeling the front brake flex lines might be a tad short, which became obvious on a trial run checking lock-to-lock turning. The 13.0" front disc versions of these flex hoses were several inches longer and routed completely differently on the control arm, so we got new lines from the later front disc/rear drum 1/2 ton truck and they bolted on perfectly. The guys then bled fresh DOT 3 brake fluid through the system and off we went on a test drive.

Left: New rear with thicker 13" rotors and upgraded twin piston calipers. Right: Upgraded front 13.0" (+1.0") diameter Powerstop rotor and caliper

Ryan noted a "long pedal" on the stops during his test drive but this truck always had a long and mushy pedal, so the new set-up might be suffering from a worn out master cylinder. We will swap to the later SUV master cylinder and see if that helps alter the hydraulic proportioning for the extra rear caliper pistons that were added, but it could just be a crappy 240K mile master cylinder showing its age. The pedal is finally firm, just a little long on travel. The truck STOPS VERY WELL now, with smoother and shorter stops than we've ever seen. Very happy with the results after a week of driving it, too.

The shop truck as of December 3rd, with the new 13" slotted/drilled/plated brake rotors and red Powerstop calipers

All told we spent around $700 for all of the parts, which included new rotors, calipers, sliders, pads and lines. Installation would take about 3 hours of labor, if you had all of the right parts to start with (which we didn't this first time, heh). This brake upgrade was considerably less costly than the cheapest BBKs we could find, and the fit and function was perfect. If anyone is interested we might offer this brake system upgrade for other GMT800 trucks like our's. After we do the SUV master cylinder update (near future) we will see if the pedal shortens up a bit, at which time we will offer this kit for sale.


So I've been sticking this "What's Next" section in all of my project posts lately... what is the next mod, event, planned repair, etc? Well this truck still needs some repair work, and the budget for upgrades to this truck is getting tighter, so its hard to say what the next thing will be. The new windshield we installed back in May took a solid rock hit at 75 mph on the GWB Turnpike less than 3 weeks after it was installed and cracked badly, so that needs to be re-replaced, yay. The rear drop shackles that somebody previously installed are still sticking and clunking within 2 days of being greased, so we have got to look at that.

I'd still really like to get lower the altitude a bit more with drop spindles, new rear springs and a C-notch kit installed on the frame, and for some light towing it has to get some helper air bags... it just snowballs from there. That set of upgrades is going to keep getting pushed back until we do some more pressing repairs. The drivetrain is starting to show its age, and with over 240,000 miles it should likely get some attention before we throw any more optional upgrades to it. The 4L60-E 4-speed automatic transmission is giving me hints that it needs a rebuild, but we will try a trans fluid and filter change first. And the 5.3L motor is just feeling a little tired. This 1999 model had the earliest and least powerful (1999-2003 5.3 made 285 hp) version of the 5.3L "LM7" V8, so almost anything newer would be an upgrade (even the smaller 4.8L made the same 285 hp from 2004-2006). I'd really like to get a fresh longblock into this truck, and it would be really nice to use an all-aluminum 5.7L LS1 block from a Camaro or Corvette while we're at it (350 hp) for a power boost, too. Honestly I have a lot more plans for this truck than there is money to pay for them, so we'll just deal with issues as they come.

Left: The larger 13" diameter rotors still look small inside 20" wheels. Right: An aluminum LSx longblock would save 80+ pounds

The biggest hangup I still have is the hideous aftermarket front grill insert, which has to go. As I mentioned earlier I want to upgrade to the later 2003-06 GMC front grill, which means a new bumper and lower fascia are needed as well (the lower shape of the GMC grill is different from 2003-2006). And all of the lights on the front (headlights, turns, fogs) on this truck are frosty and/or broken, and with the replacement bits are so cheap we might as well upgrade those at the same time. We can get all of this from the aftermarket for fairly cheap, except for the GMC logo which you can only get from a dealer. I have the new GMC logo (which was missing on this truck), just need to spend another $350 or so to get all of the rest of the new front end parts, then the plastic lower fascia will need paint. Then I'd have to decide if we are going to keep this body color (that I hate), or respray the whole truck in a different hue? That's an expensive decision so I will keep kicking the can down the road in the mean time.


Last edited by Fair!; 07-03-2017 at 09:20 AM.
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